This invention generally relates to medical devices, such as drainage stents and catheters.
Medical devices used for draining fluids from body cavities are generally made of plastic tubing. The tubing is often pre-formed on one or both of its ends to a geometry designed to maintain or anchor the device in position within the body. Medical devices of this type are commonly placed through a ureteroscope, laprascope, or endoscope and into lumens and/or body orifices. In the case of abscess catheters, placement generally occurs percutaneously through a puncture of the external dermis and musculature. In most cases, however, a guidewire is first passed through the orifice or puncture to the desired drainage site, around or through obstacles if required. The medical device is then placed over the guidewire through a lumen running the full length of the device. This straightens the anchoring geometry to ease and allow insertion. After insertion, the guidewire is pulled out through the device""s proximal end. Once the guidewire is removed from the body, the anchoring geometry assumes its natural, pre-formed shape to retain the device in position within the body of the patient.
Some medical devices use coils or pigtails as anchors in an open area of the anatomy, such as the renal pelvis of a kidney or abscessed area within a body cavity. These types of anchors allow the device (such as a ureteral drainage stent) to maintain its position within the body by blocking its migration through thinner tract openings. Another type of anchoring mechanism is commonly known as a malecot. Some other devices, such as biliary stents, use one or more barbs (formed, for example by partially skiving a tube in a longitudinal direction). Some biliary stents use barbs for retention in the biliary tract.
Known anchoring mechanisms used with medical devices can fail. For example, internal forces from involuntary bodily functions (such as peristalsis and other secretory forces, as well as patient movement) can force the device out of its intended position within the body. In addition, doctors typically recommend catheter and stent anchoring or retention structures fabricated from softer materials to enhance patient comfort. These softer materials generally have lower retention strengths as compared to more rigid materials. Also, the lower strengths of these softer materials limits the size of holes that can be formed in the medical device to help drain fluid from the body of a patient.
The present invention provides significantly increased strength to retention structures while also maintaining patient comfort. With the invention, softer materials can be used to maximize patient comfort, and reinforcement of these soft materials affords greater retention properties. Examples of devices that can include retention structures according to the present invention include, but are not limited to, a drainage catheter, a ureteral stent, a urethral stent, a biliary stent, and a prostatic stent.
In general, one aspect of the present invention relates to a medical device comprising an elongated member and a reinforced retention structure. The elongated member comprises a flexible material and defines a lumen extending therethrough. The reinforced retention structure extends from the elongated member and comprises an elastic member and the flexible material.
The elastic member may be embedded within the flexible material, or bound to a surface of the retention structure such as the inner or outer wall of the retention structure. The retention structure may extend from the distal or proximal portions of the device, lie between the distal and proximal portions in a middle portion, or exist in or on two or more portions of the device.
As used herein, xe2x80x9cdistal portionxe2x80x9d refers to the portion of the medical device furthest away from the medical operator inserting the device within the open or abscessed area of the anatomy, such as the portion in and/or near the kidney. xe2x80x9cProximal portionxe2x80x9d refers to the opposite portion of the device closest to the medical operator, such as the portion in and/or near the urinary bladder. xe2x80x9cMiddle portionxe2x80x9d refers to the portion of the medical device that lies between the distal and proximal portions.
In some embodiments, at least one large drain hole slot is formed through the wall of the retention structure. The use of the elastic member in the retention structure eliminates the risk that the retention structure will collapse on itself because of the size of the drain holes. Alternatively or additionally, the elastic member may extend into the elongated member. Because of the stability provided by this configuration, a large drain hole slot may be cut into the elongated member in place of typical smaller drain hole configurations. Also, the elastic member increases the radiopacity of at least the retention structure, thereby enhancing the locatability of the device (or at least the retention structure) using flouroscopy.
The extension of the elastic member into the elongated member also enhances pushability of the device during insertion into a body of a patient. The elastic member prevents the device from kinking as it moves within the body. In one embodiment, the elastic member may be removable from the elongated member after insertion. Under this construction, two separate elastic members reside in the retention structure and the elongated member. The length of the elastic member disposed in the elongated member exceeds the length of the device. After insertion of the device into the body of the patient, the operator proximally pulls the elastic member residing in the elongated member from the patient""s body. The elastic member residing in the retention structure remains in place.
The shape of the retention structure and its positioning with respect to the elongated member can vary in different embodiments according to the invention. The retention structure may be formed integrally with the elongated member or it may be affixed to the elongated member. A retention structure may be located anywhere along the length of the elongated member. Also, two or more retention structures may be disposed along the length of the elongated member.
In one embodiment, a elastic member is pre-formed to a curved shape and disposed within the wall of a plastic tubing. The curved shape may be a retention structure with a single turn, a retention structure with two or more turns, or simply a J curl. In another embodiment, a plurality of lengths of a pre-formed elastic material can be positioned longitudinally in the wall of a piece of tubing surrounding a central lumen. Portions of the tubing can then be cut longitudinally in between the superelastic pieces to form the arms of a malecot. In another embodiment, a dual-lumen tube is partially skived at one end into a barbed configuration. A preformed curved piece of elastic material is secured in the skived portion for added strength.
In other embodiments, one or more elastic rings radially protruding from the elongated member and containing a reinforcing superelastic ring and a flexible material may be formed or disposed along the elongated member as a retention structure. By varying the size of the rings, the device can accommodate body cavities of different shapes and sizes and work in maintaining the lumen of the tube wide open. The elastic ring or rings may be constructed from a variety of flexible materials, such as elastomeric compounds. Materials like these combine rigidity and the softness necessary for patient stability and comfort.
In all of the above-described embodiments, a plurality of drain holes may be cut into the elongated member and/or retention structure to maximize drainage. Alternatively or additionally, large drain hole slots can be cut into the elongated member and/or retention structure depending on the placement of the elastic member.
In other aspects, the invention involves methods of placing medical devices, such as the devices previously described. A method of placing a medical device of the invention into the body of a patient comprises providing the device, collapsing the retention structure and inserting the device into a patient""s body to release the retention structure, and thereby deploy the medical device in the body.
In another aspect, the invention involves methods of making medical devices of the present invention. A method of making such a device comprises extruding an elongated member made of a flexible material and incorporating a pre-formed elastic member to the flexible material by embedding the elastic member within the flexible material or by binding the elastic member to a surface or groove of the flexible material to form a reinforced retention structure.
The foregoing and other objects, aspects, features, and advantages of the invention will become more apparent from the following description, drawings, and from the claims.